High index of refraction nanosphere coatings for light trapping in crystalline silicon thin film solar cells

Dielectric nanospheres have emerged as a promising candidate for enhancing absorption in thin film photovoltaics. In this paper, we utilize numerical electrodynamic simulations to investigate the absorption enhancements achievable in crystalline Si (c-Si) thin films of thicknesses from 100 to 2000 nm from 2-dimensional close-packed silica (SiO2), silicon nitride (Si3N4), and titania (TiO2) nanosphere array coatings. We demonstrate that dielectric nanospheres can enhance the absorption in c-Si thin films by coupling incident light to transverse electric (TE) waveguide modes in the c-Si thin film. While SiO2 nanosphere arrays may achieve enhancements of less than 10% compared to ideal double pass c-Si thin films, higher index of refraction nanospheres confine light more strongly such that more nanosphere resonances may couple to waveguide modes in the c-Si. Si3N4 nanospheres may enhance ultimate efficiencies by over 40% for thicknesses <800 nm and TiO2 nanospheres by over 50% for thicknesses <700 nm compared to thin film structures with perfect anti-reflection coatings. This light trapping approach increases the absorption in the photoactive region without introducing additional surfaces or interfaces that increase surface recombination. (C) 2014 Elsevier Ltd. All rights reserved.